The present invention relates to an image forming apparatus comprising an electric writing device of which a substrate is arranged in elastic contact with a latent image carrier and which forms an electrostatic latent image onto the latent image carrier by writing electrodes disposed on the substrate.
Among conventional known image forming apparatuses, there is a type of using a large number of needle electrodes to form an electrostatic latent image onto a latent image carrier. In an image forming apparatus of this type of using needle electrodes, an electrostatic latent image is formed onto a latent image carrier by discharge from the needle electrodes. The needle electrodes are employed as discharge portion of this image forming apparatus because such a needle electrode can discharge at the lowest possible starting voltage and has an acute tip that is preferable in terms of improving the image resolution. Generally, the needle electrodes are arranged to have a slight space from, i.e. in non-contact with, the latent image carrier and the formation of an electrostatic latent image onto the latent image carrier is conducted by discharge phenomenon.
However, variation of starting voltage for discharge due to fluctuation in the space directly causes the scatter in potential of the electrostatic latent image, leading to major image defects such as linear stains, irregularities, interruption, blur, and/or dusts. Accordingly, to stably keep the space constant, the needle electrodes are required to have high precision and high rigidity and a holding member of positioning and supporting the needle electrodes is also required to have high precision and high rigidity. In addition, the needle electrodes should be precisely positioned on a bus line of the latent image carrier in the circumferential direction of the latent image carrier. If not, the fluctuation in the space should be occurred and thus uniform charge can not be ensured. Further, run-out of the rotational axis of the latent image carrier is sure to cause fluctuation in the space. For this, spacers are provided for controlling the space. However, in case of high-speed printing in which the latent image carrier rotates at a high ratio, it is hard or impossible to keep the space constant due to vibration. As a result, the printing speed should be set at a lower speed.
As a means for solving the aforementioned problems, an image forming apparatus has been proposed in Japanese Patent Publication No. S63-45104 (hereinafter, ""104B publication), in which needle electrodes are kept in contact with a latent image carrier coated by an organic glass and lubricant oil is applied to the latent image carrier to prevent wearing or damage of the latent image carrier due to the contact of the needle electrodes.
However, the invention of ""104B publication has another problem of wearing of the needle electrodes. The wearing of the needle electrodes causes variation in starting voltage for discharge, leading to change in size of the electrostatic latent image and change in charged potential. Since application of oil to the latent image carrier is necessity for reducing the wearing, developing powder such as toner can not directly deposited so that the latent image carrier can only functions as an intermediate image transferring medium.
As mentioned above, the type of using a large number of needle electrodes has a problem that scatter in potential of an electrostatic latent image is easily caused so that the latent image resolution is varied with time, thus deteriorating the quality of obtained images. Since a holding member and/or a positioning member having high precision are required for holding and positioning the needle electrodes and the latent image carrier and the space therebetween, there is also a problem that the apparatus should be complex and large. There are still problems that the electrodes and the latent image carrier should be damaged for a short period of time due to high contact pressure of needle-type electrodes, that high-speed printing is hardly achieved, and that the apparatus should be large because of the use of the latent image carrier as an intermediate image transferring medium.
To solve these problems, the applicant of this application has proposed an image forming apparatus comprising an electric writing device of which a substrate is arranged in elastic contact with a latent image carrier and which forms an electrostatic latent image onto the latent image carrier by writing electrodes disposed on the substrate. According to this image forming apparatus, the electrodes receive writing signals to form an electrostatic latent image on the latent image carrier. During this, the contact between the substrate and the latent image carrier is stabilized so as to enables homogeneous writing by application of charge, thereby obtaining a high-quality image without image irregularities nor linear stains.
However, the image forming apparatus mentioned above has some problems. As shown in FIG. 9 as will be described later, in the image forming apparatus, a length L between a distal electrode 3bR of the writing electrodes 3b and a side edge of the substrate 3a is required to be so long as to stabilize the contact of the distal electrode 3bR. Without enough length L, the pressing force onto the distal electrode 3bR and the writing electrodes near the distal electrode 3bR against the latent image carrier 2 should be smaller than that of the writing electrodes located at a middle portion. In this case, homogeneous application of charge for writing can not be achieved. On the other hand, in a cleaning device 7 disposed downstream of a transferring device 6, it is impossible to completely seal toner at contact boundary faces between a cleaning blade 7a and an end seal 7b so as to produce leakage toner T which adheres to the latent image carrier 2. Because of the great length L, however, the leakage toner T passes under the substrate 3a so as to adhere to contact portions between the writing electrodes 3b and the latent image carrier 2, causing variation in the gap between the electrodes and the latent image carrier 2. This variation leads to image irregularities.
As shown in FIG. 11(A), in a developing device 4 arranged around the periphery of the latent image carrier 2 as well as the electric writing device 3 and the transferring device 6, it is impossible to completely seal toner at contact boundary faces between a toner control blade 4c and an end seal 4d to produce leakage toner T which adheres to the latent image carrier 2 as shown in FIG. 11(B). Because of the great length L, however, the leakage toner T passes under the substrate 3a so as to adhere to contact portions between the writing electrodes 3b and the latent image carrier 2, causing variation in the gap between the electrodes and the latent image carrier 2. This variation leads to image irregularities.
In order to prevent this problem, the width of the electric writing device 3 is set to be smaller than the width of the toner control blade 4c as shown in FIG. 13. In this case, a transferring roller of the transferring device 6 is required to have a width obtained by adding an allowance for the sheet feeding accuracy to the width of the maximum recording sheet size. To prevent the leakage toner T from adhering to the transferring roller, the width of the transferring roller should be smaller than that of the toner control blade 4c. The width of the latent image carrier 2 should be the largest among the other components mentioned above to achieve stable contact among the components. When the width dimensions are set in the manner as mentioned above, remainder toner adheres to the transferring roller in a region a between an end of the largest recording sheet and an end of the transferring roller. In addition, even after transfer to the recording sheet, remainder toner exists on the latent image carrier 2 in a region xcex2 between the end of the transferring roller and the end of the toner control blade 4c. Further, remainder toner in a region xcex3 between the end of the transferring roller and the end of the electric writing device 3 adheres to the end of the electric writing device 3 little by little, whereby the contact of the writing electrodes 3b near the end becomes unsteady with time, thus causing variation in the gap between the electrodes and the latent image carrier 2. This variation leads to image irregularities.
In order to solve this problem, the applicant of this application has proposed an image forming apparatus comprising a writing device of which a substrate is arranged in elastic contact with a latent image carrier and which forms an electrostatic latent image onto the latent image carrier by writing electrodes disposed on the substrate. According to this image forming apparatus, the electrodes receive writing signals to form an electrostatic latent image on the latent image carrier. During this, the contact between the substrate and the latent image carrier is stabilized so as to enables homogeneous writing, thereby obtaining a high-quality image without image irregularities nor linear stains.
However, this image forming apparatus still has a problem that even residual toner after transfer is removed by a cleaning means, toner leaks at their ends and the leakage toner passes under the substrate of the writing device and adheres to contact portions between the writing electrodes and the latent image carrier because the substrate of the writing device is in elastic contact with the latent image carrier. The toner adhering to the contact portions between the writing electrodes and the latent image carrier causes variation in the gap between the electrodes and the latent image carrier. This variation leads to image irregularities.
It is an object of the present invention to stabilize the potential and size of an electrostatic latent image so as to obtain a high resolution and high quality image and to reduce the friction of electrodes and a latent image carrier so as to improve the durability.
It is another object of the present invention to prevent toner leaking at end seals of a developing device, a cleaning device, and the like from adhering to writing electrodes so as to prevent error in writing an electrostatic latent image.
It is still another object of the present invention to prevent leakage toner from causing variation in gap between the writing electrodes and the latent image carrier so as to prevent occurrence of image irregularities.
It is further still another object of the present invention to prevent remainder toner left on non-image portions at both ends of a developing means from adhering the writing electrodes so as to prevent error in writing an electrostatic latent image.
To achieve the aforementioned object, an image forming apparatus comprises a latent image carrier, a writing means having a plurality of writing electrodes which are aligned in the axial direction of said latent image carrier and arranged in contact with or proximity to said latent image carrier to form an electrostatic latent image on said latent image carrier, a developing means for developing the electrostatic latent image on said latent image carrier, and is characterized in that the contact width of said writing means relative to said latent image carrier is set within the width of a toner carrying portion of said developing means confronting said latent image carrier. In an image forming apparatus further comprising a cleaning means which is arranged in contact with said latent image carrier to remove residual toner, the contact width of said writing means relative to said latent image carrier is set within the contact width of said cleaning means relative to said latent image carrier.
In an image forming apparatus further comprising a transferring means, a relation L1 less than L2 and a relation L1 less than L3 are satisfied and a relation L1 less than L3 less than L2 is satisfied, wherein L1 is the contact width of said writing means relative to said latent image carrier, L2 is the width of a toner carrying portion of said developing means confronting said latent image carrier, L0 is the width of said latent image carrier, and L3 is the width of said transferring means.
In an image forming apparatus further comprising a charge removing means for removing charge from residual toner on said latent image carrier, at least the width of a charge removing portion of said charge removing means is set to be larger than the contact width of said writing means relative to said latent image carrier, and the width of a charge removing portion of said charge removing means is set to be larger than the width of a toner control portion of said developing means.
In an image forming apparatus further comprising an intermediate transferring member for temporally transferring a toner image obtained on said latent image carrier by the deploying and a cleaning means which is arranged in contact with said intermediate transferring member to remove residual toner, wherein the toner image on said intermediate transferring member is transferred to a recording medium, at least the contact width of said cleaning means relative to said intermediate transferring member is set to be larger than the contact width of said writing means relative to said latent image carrier, at least the width of said latent image carrier is set to be larger than the width of said writing means and the contact width of said cleaning means relative to said intermediate transferring member is set to be larger than the width of said latent image carrier.
In an image forming apparatus further comprising a transferring means for transferring a toner image obtained on said latent image carrier by the deploying to a recording medium fed by a recording medium feeding means, and a cleaning means which is arranged in contact with said recording medium feeding means to remove residual toner, at least the contact width of said cleaning means relative to said recording medium feeding means is set to be larger than the contact width of said writing means and least the contact width of said cleaning means relative to said recording medium feeding means is set to be larger than the width of said latent image carrier.